The goal of the proposed research is to increase our knowledge of the role of the kidney in conjugating endgenous compounds, drugs and environmental toxins. The relation between in vivo renal conjugate synthesis and plasma concentrations of ionized and non-ionized precursors will be studied in isolated perfused human kidneys and in in vivo kidneys of rats. The effect of drugs which alter uric acid excretion in man will be studied in the chicken by use of the Sperber technique. In addition, the effects of L-dopa, its intrarenal metabolites and the effect(s) of vanadium on the peritubular and luminal excretory transports of uric acid will be determined by experimentally differentiating between: (a) the renal excretory transport of urate formed during the transfer of a precursor across the renal cell and, (b) the renal excretory transport of preformed urate.